Project Summary/Abstract Cilia are microtubule based organelles found on most cells in the mammalian body. Until recently, cilia were thought to be relatively unimportant for normal health;however, studies in humans, mice, and model organisms have demonstrated that defects in cilia signaling or assembly cause severe disease pathologies called ciliopathies. In the kidney, ciliary dysfunction results in renal failure due to the formation of large cysts. In part this is due to loss of function of the polycystins, proteins involved in human polycystic kidney disease (PKD), which localize to cilia and are required for the mechanosensory role of cilia. Unexpectedly, inducible loss of cilia in the kidney of mice revealed the severity of the cystic pathology is influenced by when cilia function is disrupted. If cilia loss occurs during late gestation cysts develop very rapidly. In contrast, induction of cilia loss in adults does not result in cysts until a year after they are disrupted. However, once they begin to form in the adults they progress rapidly. Based on this observation, the initial goal of this proposal is to dissect the molecular and cellular basis behind the delay in cyst formation and the switch to rapid cyst expansion later in adult life. The effect of cilia dysfunction on cell proliferation, cell death, and the activity of signaling pathways affected in cystic kidney disease are being explored. In addition to the loss of cilia, there are several mouse models where kidney cysts develop with cilia that are either too long or too short, suggesting that cilia length may also be important. Thus, the goal of the second aim is to evaluate how cells control cilia length. As part of this analysis, the effect of excessively long cilia on signaling activity and on coordinating the levels of intracellular signaling molecules associated with cyst development will be determined. Finally, there are several proteins associated with human cystic kidney disorders, such as nephronophthisis and Meckel syndrome, which localize to the basal body, a structure at the base of cilia from which cilia assemble. Importantly, these basal body proteins are highly conserved and also localize to the base of cilia in organisms such as C. elegans. As seen in humans, mutations in these genes in C. elegans did not alter cilia morphology. However, these mutants exhibit behavioral phenotypes indicating that cilia mediate signaling activity is impaired. Thus, the third aim is to utilize C. elegans as a model system to explore the role of these proteins in the basal body signaling complex that is required for normal cilia signaling. Finally, C. elegans will be used to identify mutations that modify the behavioral phenotype of one of the basal body mutant proteins. This will allow the identification of novel proteins which function as part of the basal body signaling complex. Overall, these data will lead to a better understanding of how mutations affecting cilia and basal body signaling activity contribute to ciliopathies such as cystic kidney diseases. Project Narrative Mutations in several proteins which localize to cilia or the basal body at the base of cilia result in severe pathologies referred to as ciliopathies;however, the function of most of these proteins and the signaling pathways affected remain unresolved. Thus, the objectives of the proposal are to explore the cellular and molecular mechanisms involved in disease pathogenesis caused by disruption of cilia signaling activity, to understand how cilia generated signals are regulated, and to identify novel components that function in the cilia/basal body signaling pathways. These data will provide important and novel insights into how disruption of cilia and basal body signaling can cause human disorders such as cystic kidney disease.